1. Field of the Invention
The present invention relates to an internal combustion engine.
2. Description of the Related Art
As an exhaust gas after-treatment device arranged in the exhaust passage of an engine, there is known an NOx absorbent which absorbs the NOx in exhaust gas when. the air-fuel ratio of the exhaust gas is lean and releases and reduces the absorbed NOx when the air-fuel ratio of the exhaust gas becomes the stoichiometric air-fuel ratio or rich. In such an exhaust gas after-treatment device, the air-fuel ratio of the exhaust gas is temporarily made rich before the NOx absorption capability of the NOx absorbent becomes saturated so as to make all of the NOx absorbed in the NOx absorbent be released from the NOx absorbent and reduced.
Fuel, however, contains sulfur. Therefore, the exhaust gas contains SOx. This SOx is also absorbed by the NOx absorbent. This SOx is not released from the NOx absorbent just by making the air-fuel ratio of the exhaust gas rich. To make the SOx be released from the NOx absorbent, it is necessary to raise the temperature of the NOx absorbent. Therefore, there is known an internal combustion engine wherein when the temperature of the NOx absorbent should be raised, additional fuel is injected in the expansion stroke or exhaust stroke in addition to the main fuel injected during the suction stroke and that additional fuel is made to burn in the NOx absorbent so as to raise the temperature of the NOx absorbent (see Japanese Unexamined Patent Publication (Kokai) No. 9-32619).
In this way, in an internal combustion engine, it is sometimes necessary to raise the temperature of the exhaust gas after-treatment device. In this case, in an internal combustion engine, there are sometimes cases where it is necessary to rapidly raise the temperature of the exhaust gas after-treatment device. Further, there are sometimes cases where conversely it is necessary to slowly raise the temperature of the exhaust gas after-treatment device. That is, it becomes, necessary to be able to change the temperature raising rate of the exhaust gas after-treatment device in accordance with demand. In the above known internal combustion engine, however, when raising the temperature of the exhaust gas after-treatment device, a predetermined injection pattern determined by the operating state of the engine was used. As a result, there was the problem that it was not possible to freely change the temperature raising rate of the exhaust gas after-treatment device in accordance with demand.
An object of the present invention is to provide an internal combustion engine capable of raising a temperature of an exhaust gas after-treatment device at a temperature raising rate which is required for the exhaust gas after-treatment device.
According to the present invention, there is provided an internal combustion engine having a combustion chamber and an exhaust passage, the engine comprising fuel injection means for injecting an auxiliary fuel into the combustion chamber, in addition to a main fuel, in accordance with necessity to produce unburned hydrocarbons; an exhaust gas after-treatment device arranged in the exhaust passage, a temperature of the exhaust gas after-treatment device rising when a temperature of exhaust gas rises and rising when unburned hydrocarbons are supplied to the exhaust gas after-treatment device; and injection control means for retarding an injection timing of the main fuel when the temperature of the exhaust gas after-treatment device should rise, as compared with the case where the temperature of the exhaust gas after-treatment device should not rise, at least two injection patterns, which are different in at least one of an amount of retardation of the injection timing of the main fuel and injection timing of the auxiliary fuel, being determined in advance to raise the temperature of the exhaust gas after-treatment device, the injection control means choosing any one of the injection patterns in accordance with a demand for a temperature raising rate of the exhaust gas after-treatment device and injecting fuel in accordance with the chosen injection pattern when the temperature of the exhaust gas after-treatment device should rise.